span multiple days,months - if this, calculate one way if not calculate another

[Anonymous]

I am trying to calculate a field (Prod Per Hour) .  If the date is >= 3-1-2017 use this calculation, if its < 3-1 use another calculation.

In doing so I can select the   year,  month or days.      If I choose one month or day, I can get the correct results but if spanning months/days I can not.   How can I get it to work with multiple selections?